Cyclotron tuning apparatus



Feb. 16, 1954 w. w. SALISBURY 2,669,653

CYCLOT RON TUNING APPARATUS Filed April 12, 1950 3 Sheets-Sheet l774451? MOTOR IN V EN T 0R. W/NF/ELD h/ SAL/5811p) A TTOP/VEY Feb. 16,1954 w. w. SALISBURY 2,669,653

CYCLOTRON TUNING APPARATUS Filed April 12, 1950 3 Sheets-Sheet 2INVENTOR.

VV/NFIEL 0 W. SAL/seam A rramvev Feb. 16, 1954 w. w. SALISBURY 2,669,653

CYCLOTRON TUNING APPARATUS Filed April 12. 1950 3 Sheets-Sheet 3 22INVENTOR.

M/VF/E'LO W 5,4U5'8l/RY ATTORNEY Patented Feb. 16, 1954 GYCLOTRON TUNINGAPPARATUS Winfield W. Salisbury, Cedar Rapids, Iowa, as-

signor to Collins Radio Company, Cedar Rapids, Iowa, a corporation ofIowa Application April 12, 1950, Serial No. 155,511

8 Claims. (01. 250-27) This invention relates in general to cyclotronoscillators, and in particular to a method of starting the cyclotron toget it past the condition in which the dees are detuned due to electronvibration in the neighborhood of the dees.'

Although generally the chamber of a cyclotron is-pumped to asubstantially low pressure there are always some residual particles leftin the chamber and some of these particles become charged. In order tooperate a cyclotron, an alternating voltage must be impressed betweenthe dees to accelerate ions. The charged particles initially in thecyclotron chamber have a tendency to detune the dee circuit, and thusmake it difficult to bring the dees up to the operating voltage. Thereason for the detuning by the charged particles is that if the particleis a free electron it will oscillate between a dee and the wall of thechamber as the initial relatively small voltage is applied to the dees.accelerated it absorbs energy from the dee, and when it strikes a gasparticle or the walls, it gives energy to them. When a large number ofthese charged particles are oscillating and fail to reach the wall ofthe cyclotron, or the dee, and give up enough charge to make themneutral, the entire dee system is badly detuned. As soon as the voltagebetween the dees builds up to a high enough value substantially all ofthe residual particles will contact either the dees or the walls of thecyclotron and thereby lose theircharge. I

When this condition exists, the charged particles no'longer present anyinterference to the operation of the dees and they oscillate at the trueresonant frequency. order to get optimum operating conditions a drivingoscillator should be tuned to the driven circuit. The dees form aresonant driven circuit and the driving energy is furnished by theoscillator. Since the dees are initially resonant at some frequencyother than the operating resonant frequency, due to the above describedphenomena, it is advantageous to be able to detune or' change thefrequency of the driving oscillator during starting conditions and tochange it back to the dee-operating resonant frequency after the voltagehas been raised.

It is an object of this invention, therefore, to provide a novel drivingoscillator for a cyclotron which is automatically tunable and which willadjust itself to overcome the initial detuning caused by the residualcharged particles in the cyclotron chamber.

, Another object of this invention is'to provide means whereby thedriving oscillator of the cyclo- As the charged particle is It is wellknown thatin 2 I tron may be automatically tuned to a frequency whichwill drive the dees above a critical voltage so that the detuning effectcaused by the residual charged particles may be overcome and which willthen change the frequency of the driving oscillator to a frequency nearthe resonant frequency of the dee system.

Yet another object of this invention is to provide means for preventingthe oscillator tubes of a cyclotron from drawing excessive grid current.

A feature of this invention is found in the provision for a tunableelement comprising an inherent inductance and capacitance which may beconnected in the oscillating circuit of a driving oscillator for varyingthe frequency.

' Further objects, features, and advantages of this invention willbecome apparent from the following description and claims when read inview of the drawings; in which Figure l is a schematic illustration ofthe dees of the cyclotron with a driving oscillator connected theretoand an oscillator tuning element connected for automatically tuning theoscillator to the desired frequencies;

Figure 2 is a detailed isometric view of the oscillator tuning device ofthis invention;

Figure 3 is a schematic illustration of a modification of the invention;and Figure 4 is a schematic of another modification.

Referring to Figure 1, a pair of cyclotron dees Ill and H are shown withtheir stems 8 and 9 connected to the shorting bar it which is' of copperor other suitable material. It is to be understood that the dees formpart of a conventional cyclotron of the type well known to those skilledin the art, wherein the dees are held in a predetermined spatialrelationship between a pair of pole pieces of a direct current magnetwhich passes an exciting field at right angles past the dees. Theoperation of the cyclotron is well known and requires the introductionbetween the dees of charged particles. They are accelerated spirally dueto the action of the magneticfield from the pole pieces and'an electricalternating field which is impressed between the dees. This alternatingcurrent field is impressed across the dees by connecting an oscillator,designated generally as l3, to them. The oscillator l3 comprises thetubes I 4 and i5, respectively, which have their plates ll and isconnected together by the inductive coupling loop H). The inductivecoupling loop I9 extends down closely adjacent to the stems 8 and 9 todrive them.

' Between the mid-point 2! of the coupling loop l9 and a shorting bar I2is connected an inductonce 22. The shorting bar may be grounded. Thecoupling loop I9 is placed adjacent the shorting bar I2 and the voltageinduced in the dees is greatly increased and amplified at points furtheraway from the shorting bar and the coupling loop. For example, themaximum amplitude of the Voltage on the .dees iii and .l i will occuradjacent their accelerating ends and will'be zero at the shorting barbecause it comprises a direct short. The cathodes 23 and 24 of the tubes84 and [E are tied together and are connected to B.. .Between the grids26 and 21 of the tubes M and 16, respectively, is connected a tunable:circuitwhich comprises the interelectrode capacitances -Cl4pg 7 andCliipg and the variable inductance-capacitance 23. ClApg is the plate togridcapacitance of tube 54 and clfipg is the plate to grid capacitanceof tube it. A grid leak resistor 29 connects the mid-point of a coil 3|in the inductance-capacitance. 28 to the cathodes 2-3 and .241.

The inductance-capacitance is better shown in Figure 2Qomprisesithehousing member 32; which supports the coil-3 l. The coil 3ienters ,the housing 32 through one end thereotand emerges fromtheopposite end. th housing 32 are a plurality of shafts 33 whichextendtransversely through the coil 3 l Carried intermediate the ends ofeach shaft 33 is a disc of substantially: circular shape which may be ofcopper or other suitable material. The shafts 33 are connected togetherby the belts 35 which are attached to pulleys 3? so that if any one ofthem i moved, theothers turn correspondingly.

Th discs are .-smaller in diameter than the internal diameter of thecoil 3| and thus may be freely rotated Within the toil. A bracket 33 isconnected to the housing 32 and pivotally supports therein a shaft 39Which has attached thereto-the pulley ii. one of the pulleys 3? so thatth shafts 33 may be rotated in response to the movement of-shaft 39.When the discs 3% are alignedso that their plane is parallel to thelongitud'mal axis of the coil, maximum inductance-may be obtained fromthe coil. On the other hand, whenthe shafts 33 are rotated until theyare transvers to the coil 3!, the inductance is at a minimum because thecopper discsi i tend to short out the lines of flux be tween adjacentcoil and thus substantially de- Y crease the inductance.

A starting switch 25 starts operation of the cyclotron and closes theoscillator circuits. The discs '34 are initially adjusted relative tothe coil3l so that a large inductance is obtained. When the startingswitch 25 is engaged it ,actuates a timer zd. After a preset time thetimer closes the circuit to a drive motor at. The motor 33 is connectedtothe shaft 39 through the mechanical linkage to and thus the discs arerotated to decrease the inductance incoil 3i and to tune the oscillatorto :the docs.

Theshaft .39 may be rotated manually from .a shielded room adjacent thecyclotronif desired.

A volt-a e probe may be attached to the does to indicate when the changin inductanc should occur. It may be connected to a motor controlcircuit, not shown, which actuates the motor.

Figure 3 illustrates a modification of this in. vention wherein a relayto has been connected in series with aresistor .25. The armatureit ofthe relay is mechanically linked to a crank arm Which is connected tothe shaft 39 of the inductorcapacitorinductance12.3. 36 illustrated inFigure 1 have been eliminated.

lransversely pivoted .in

A belt 42 connects the pulley with ,Thetimer 2.6 andmotor 4 In operationthe apparatu of Figure 3 is initially set to the starting position withthe discs 34 set to their maximum inductance position. When theoscillations are initiated, the grid current becomes larger and largeruntil finally the current through th resistor 2t and the relay to issuch as to move the armature thus changing the position of the discs 35.This returns the oscillator circuit to the desired operating point. Thearmature 45 of the relay 45 will continue to be held in the closed:position even though the discs 34 have been moved to decrease theinductance for the reason that once the armature has closed, lesscurrent is reouiredto maintain it in a closed position than is necessaryto cause the closing of the relay.

Figure 4 illustrates a further modification of the invention whereininductance capacitance 28 has been eliminated and an inductive loop 48has been substituted therein. A loop 48 provides the inductancenecessary for operation of th oscillator and with the inner; electrode.capa'oitances flnpg, and .Cldpg comprises th oscillators tvnedtcircuit.A relay at has its winding 5! connected inseries with the loop and has amovable armatureEiZ which is mechanically linked to a shorting harm. W nthe cyclotron is started, the .armature52 is open and the grid current:flow through the inductive loop d8. When .the'current in the loop 135reaches a predetermined value thearmature;52 of the relay lscloses, thusshorting a portion of the loop to. This results ina decrease ininductance which in turn-causes.areduction in grid current. Thisprevents overloading of the grids of the tubes iii and i5.

It is seen, therefore, that this invention provides means forstartingthe cyclotron and driving it to a conditionvzhcre the originaldetuning, due to the residual charged particles, will be overcome andwithout subjecting the grid circuit to overload for a lon period.

Although'this invention has been described with respect to particularembodiments thereof, .it is not to he so limited as changes'andmodifications may be made therein which are within the full intendedscope as defined .by theappended claims.

I claim:

1. Ina cyclotronhaving dees which are initially detuned due to residualcharged particles within the doc chamber and in which the dees areexcited by a driving oscillator, oscillator tuning means comprising aninductance coil connected between the grids orthe oscillator tubes,support means connected to the coil, ashaft pivotally supported in saidsupport mean transversely of said coil, a generally fiat non-magneticmember connected to said shaft-within the confines of said coil, drivingmeans connected to said shaft for rotatingit relative to said supportmember, control meansoonnected to said driving means toac-.tuateitisothat thelinductanceof saidscoil maybe changed to-tune thedriving oscillator to the docs; and atimer connected'to said controlmeans to energize'it.

2. In a cyclotron having apair of .dees anda driving oscillator,means'for tuning said oscillator comprisingan inductance coil intheresonant circuit of said oscillator, a paddle supported for rotarymotion relative to sai soil, and with said paddle having a substantialareawithin said coil and rotatable about an transverse to said coil,driving means connected to said paddle to tlmethe driving oscillator tothecyclotron does.

3. Starting means for a cyclotron having .a pair of dees'and a drivingoscillator comprising, a frequency control circuit iorsaid oscillator,in-.

ductive means connected to the frequency control circuit, means forchanging the inductance of said inductance means, and cyclotron startingmeans connected to said means for changing inductance to actuate itduring the starting period.

4. In a cyclotron having dees which are initially detuned due toresidual charged particles within the dee chamber, and in which the deesare excited by a driving oscillator, automatic tuning means comprising,a frame member, an inductance coil supported in said frame member withsaid coil being connected in the resonant circuit of the cyclotronoscillator, a plurality of shafts passing transversely through saidframe, a disc member carried on each of said shafts and maintainedwithin the confines of said coil, driving means connected to saidshafts, timing means controlling said driving means, and said timeractuated by the starting switch of the cyclotron to vary the inductanceof said coil to keep the oscillator tuned to the dee during the startingcycle.

5. Starting means for a cyclotron having dees which are initiallydetuned due to the residual charged particles in the dee chamber and inwhich the dees are excited by the driving oscillator, automatic tuningmeans comprising a bracket member, a coil supported in said bracket, andwith said coil connected in the resonant circuit of said oscillator. aplurality of transverse shafts pivotally supported in said frame andpassing transversely through said coil, a disc member carried on eachshaft within the confines of said coil, flexible means interconnectingsaid shafts so that when one is rotated they all will rotate, drivingmeans connected to one of said shafts, a timer connected to said drivingmeans to actuate the inductance change, and the starting switch for saidcyclotron connected to said timer so that the timer will actuate themotor to maintain the oscillator tuned to the dee system of thecyclotron.

6. In a particle accelerator having electrodes which are initiallyde-tuned, and in which the dees are excited by a driving oscillator,automatic tuning means comprising, variable inductance means, a relaycircuit connected in the grid circuit of the driving oscillator, and anarmature of said relay connected to said variable inductance means tovary it in response to energization of said relay.

7. In a particle accelerator having electrodes which are initiallyde-tuned and in which the dees are excited by a driving oscillator,automatic tuning means comprising an inductive loop connected in seriesbetween the grids of the oscillator tubes, an electromagnetic meansconnected in series with said loop, a shorting bar movable to a firstposition disengaged with the loop and movable to a second position inengagement with the loop, mechanical linkage between the bar and saidelectromagnetic means to move the shorting bar from the first to thesecond position in response to actuation of said electromagnetic means.

8. Means for automatically tuning the driving oscillator of a cyclotronhaving an inductive loop between the grids of the oscillator tubescomprising, a shorting bar movable into and out of engagement with saidloop, a relay connected in series with said loop, a movable armatureconnected to said relay, and mechanical linkage connecting said shortingbar to said armature to move it from a first position out of engagementwith said loop to a second position into engagement with said loop.

WINFIFLD W. SALISBURY.

References Cited in the file of this patent UNI TED STATES PATENTSNumber Name Date 1,510,945 Lewis Oct. 7, 1924 1,571,405 Goldsmith Feb.2, 1926 2,265,390 Moore Dec. 9, 1941 2,473,188 Al'bin June 14, 19492,492,324 Salisbury Dec. 27, 1949 2,517,948 Warren Aug. 8, 19502,544,832 Hadley Mar. 13, 1951

